Internal combustion engines are used extensively for a variety of purposes. The transportation infrastructure relies almost exclusively on the use of engines to provide power for mobility. Electrical power generation also relies heavily on internal combustion engines.
The prolific use of engines in our society has created a number of issues, one of which is the ever-increasing amounts of combustion by-products being emitted. Although today's engines operate with much lower emission levels than previous generations of engines, the rapidly increasing numbers of engines being used creates the need to reduce emission levels even more.
Governments around the world recognize this problem and are taking regulatory steps to address the emission levels of engines. For example, levels of oxides of nitrogen (NOx), hydrocarbons (HC), carbon monoxide (CO), and smoke, among others, must be reduced drastically to meet evolving government standards.
Spark ignition engines, by the nature of their operation and the types of fuel used, tend to produce low levels of NOx and particulate emissions. Compression ignition engines, for example diesel engines, generally produce high levels of NOx and particulate emissions. Diesel engines, however, are still popular in use because they provide higher thermal efficiency than their spark-ignition counterparts, and thus offer higher power output for work applications.
Engines that operate in homogeneous charge compression ignition (HCCI) mode have generated much interest due to the potential to operate at high fuel efficiency while generating low combustion emissions. HCCI engines differ from conventional diesel compression ignition engines in that diesel engines ignite fuel that is rich, i.e., highly concentrated in an area in a combustion chamber, while HCCI techniques create a dispersed homogeneous fuel/air mixture by the time of combustion. Combustion of a homogeneous fuel/air mixture allows an engine to operate such that emission by-products are significantly reduced.
The theory of HCCI mode operation has not been met by the reality, however. It has proven to be extremely difficult to create a desired homogeneous mixture of fuel and air and still control operation of the engine. For example, it is very difficult to control the timing of combustion when introducing a homogeneous mixture into a combustion chamber. Past attempts by others has only resulted in partial success under low load, e.g., one half load or less, conditions. In U.S. Pat. No. 6,286,482, Flynn et al. recognize this issue and only operate an engine in PCCI mode (which is equivalent to HCCI) under low to medium load conditions. Operation switches to spark ignition mode at high loads. Yanagihara, in a paper entitled “Ignition Timing Control at Toyota ‘UNIBUS’ Combustion System”, limits engine operation to one half load to enable operation in HCCI mode.
The present invention is directed to overcoming one or more of the problems as set forth above.